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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Si 



magnum and the posterior articulations of the mandibles. Two dif- 

 ferent types of structure follow from this style of modification, one 

 shown in adult Hymenoptera and in the larvae of Lepidoptera, the 

 other in those orders in which a gular plate is developed. 



The morphology of the posterior surface of the hymenopteran head 

 is comparatively easy to understand, for, in the larval stages, the 

 rear aspect of the head presents the same structure as does that of 

 an adult orthopteron (fig. 36 C). In the head of the larva of Vespa, 

 for example (fig. 48 A), the details of the structure are exactly as 

 in the grasshopper. There is a distinct postoccipital suture {pos) 

 ending below in the invaginations of the posterior arms of the ten- 

 torium {pt, pt). The postocciput {Poc) is very narrow, but it forms 

 the marginal lip of the head capsule behind the postoccipital suture. 



Cd 



Fig. 48. — Development of the posterior head region in Hymenoptera. 



A, posterior surface of head of larva of Vespa maciilata. C, same of the 

 adult. D, corresponding view of head of adult Apis mellifica. 



Cd, cardo ; Lb, labium ; Oc, occiput ; Pge, postgena ; Poc, postocciput ; pos, 

 postoccipital suture ; pt, posterior tentorial pit ; St, stipes. 



The labium (Lb) is suspended from the ventral neck membrane, 

 and the cardines of the maxillae (Cd) are articulated to the ventral 

 cranial margins just anterior to the tentorial pits. 



In the adult wasp (fig. 48 B) the back of the head presents a quite 

 different appearance from that of the larva. The foramen magnum 

 is greatly contracted and is reduced to a small aperture in the center 

 of a broad occipito-postgenal field. It is surrounded by a wide post- 

 occipital collar (Poc) set off by the postoccipital suture (pos), in 

 which suture are located the posterior tentorial pits (pt, pt). The 

 labium (Lb) is detached from the neck and displaced anteriorly 

 (ventrally), and the space between its base and the neck is closed by 

 mesal extensions of the inner angles of the postgenae (Pge, Pge). 

 The articulations of the cardines (Cd) are also far removed from the 

 tentorial pits (pt, pt), and are separated from them by the interven- 

 ing bridge of the postgenae. In the wasp the postgenal bridge pre- 



